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\caption{\textbf{Effect of maternal health on twinning} {\footnotesize  Results from OLS regressions of a child's birth type (twin or singleton)  on the mother's health behaviours and conditions are displayed for women  aged 18-49. These results are summarised in figure 5 of extended data. The outcome variable is binary variable for a twin (=1) or singleton (=0)      birth, multiplied by 100, so all coefficients are expressed in terms of thepercentage point increase in twinning. Dependent variables are standardisedso coefficients can be interpreted as the percentage point change in twin  births associated with a 1 standard deviation (1 $\sigma$) increase in thevariable of interest. All models include fixed effects for age and birth   order, and where possible for gestation of the birth in weeks (panels A andB). Asterisks indicate significance levels of p-values, with: *p$<$0.1     **p$<$0.05  ***p$<$0.01. 95\% confidence intervals are displayed in        parentheses. USA data is the full sample of non-ART births from the        National Vital Statistics System from 2009-2013 (all years for which ART isrecorded).  Swedish data comes from the Swedish Medical Birth Registry,    United Kingdom data is from the ALSPAC (Avon Longitudinal Survey of Parentsand Children) panel study, Chilean data is from the ELPI (Early Life       Longitudinal Survey), and Developing Country Data is from the pooled       Demographic and Health Surveys. Further details regarding estimation       samples and variable construction are available in Methods.}}
\scalebox{0.90}{\begin{tabular}{llcllc}
 \toprule\multicolumn{3}{c}{Health Behaviours / Access} &\multicolumn{3}{c}{Health Stocks and Conditions } \\ 
\cmidrule(r){1-3} \cmidrule(r){4-6} 
Variable & Estimate & [95\% CI] &Variable & Estimate & [95\% CI]\\ \midrule 
\rowcolor{LightCyan} \multicolumn{6}{c}{\textbf{Panel A: United States} [N =13,962,330, \% Twin = 2.84]} \\ 
Smoked Before Pregnancy&-0.105$^{***}$&[-0.132,-0.078]&Height&0.626$^{***}$&[0.599,0.653]\\
Smoked Trimester 1&-0.205$^{***}$&[-0.232,-0.178]&Underweight&-0.151$^{***}$&[-0.176,-0.126]\\
Smoked Trimester 2&-0.247$^{***}$&[-0.272,-0.222]&Obese&0.035$^{**}$&[0.008,0.062]\\
Smoked Trimester 3&-0.250$^{***}$&[-0.275,-0.225]&Diabetes&-0.288$^{***}$&[-0.317,-0.259]\\
Education&0.805$^{***}$&[0.772,0.838]&Hypertension&-0.217$^{***}$&[-0.250,-0.184]\\
\rowcolor{LightCyan} \multicolumn{6}{c}{\textbf{Panel B: Sweden} [N =1,240,621, \% Twin = 2.55]} \\ 
Smoked (12 weeks)&-0.266$^{***}$&[-0.301,-0.231]&Height&0.617$^{***}$&[0.592,0.642]\\
Smoked (30-32 weeks)&-0.285$^{***}$&[-0.312,-0.258]&Underweight&-0.140$^{***}$&[-0.173,-0.107]\\
&&&Obese&-0.113$^{***}$&[-0.137,-0.089]\\
&&&Asthma&-0.015$^{*}$&[-0.033,0.003]\\
&&&Diabetes&-0.253$^{***}$&[-0.278,-0.228]\\
&&&Kidney Disease&-0.079$^{***}$&[-0.101,-0.057]\\
&&&Hypertension&-0.099$^{***}$&[-0.121,-0.077]\\
\rowcolor{LightCyan} \multicolumn{6}{c}{\textbf{Panel C: United Kingdom (Avon)} [N =2,052,338, \% Twin = 2.10]} \\ 
Healthy Foods&0.538$^{***}$&[0.256,0.820]&Height&0.399$^{***}$&[0.115,0.683]\\
Fresh Fruit&0.019&[-0.281,0.319]&Underweight&-0.161&[-0.439,0.117]\\
Alcohol (Infrequently)&-0.099&[-0.373,0.175]&Obese&-0.046&[-0.322,0.230]\\
Alcohol (Frequently)&-0.358$^{**}$&[-0.630,-0.086]&Diabetes&-0.056&[-0.328,0.216]\\
Passive Smoke&0.047&[-0.243,0.337]&Hypertension&-0.480$^{***}$&[-0.752,-0.208]\\
Smoked during Pregnancy&-0.162&[-0.448,0.124]&&&\\
Education&0.416$^{*}$&[-0.002,0.834]&&&\\
\rowcolor{LightCyan} \multicolumn{6}{c}{\textbf{Panel D: Chile} [N =26,527, \% Twin = 2.55]} \\ 
Smoked during Pregnancy&-0.329$^{***}$&[-0.568,-0.090]&Underweight&-0.199$^{*}$&[-0.407,0.009]\\
Drugs (Infrequently)&-0.006&[-0.249,0.237]&Obese&-0.269$^{***}$&[-0.443,-0.095]\\
Drugs (Frequently)&-0.163$^{***}$&[-0.196,-0.130]&&&\\
Alcohol (Infrequently)&-0.098&[-0.376,0.180]&&&\\
Alcohol (Frequently)&-0.172$^{***}$&[-0.211,-0.133]&&&\\
Education&0.466$^{***}$&[0.146,0.786]&&&\\
\rowcolor{LightCyan} \multicolumn{6}{c}{\textbf{Panel D: Developing Countries} [N =2,052,338, \% Twin = 2.10]} \\ 
Doctor Availability&0.092$^{***}$&[0.059,0.125]&Height&0.282$^{***}$&[0.251,0.313]\\
Nurse Availability&0.065$^{***}$&[0.034,0.096]&Underweight&-0.092$^{***}$&[-0.117,-0.067]\\
Prenatal Care Availability&0.109$^{***}$&[0.082,0.136]&Obese&0.062$^{***}$&[0.031,0.093]\\
Education&0.153$^{***}$&[0.122,0.184]&&&\\
\bottomrule 
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